Overexpression of Kinase-Negative Protein Kinase Cδ in Pancreatic β-Cells Protects Mice From Diet-Induced Glucose Intolerance and β-Cell Dysfunction

OBJECTIVE-In vitro models suggest that free fatty acid-induced apoptotic beta-cell death is mediated through protein kinase C (PKC)delta. To examine the role of PKC delta signaling in vivo, transgenic mice overexpressing a kinase-negative PKC delta (PKC delta KN) selectively in beta-cells were generated and analyzed for glucose homeostasis; and beta-cell survival. RESEARCH DESIGN AND METHODS-Mice were fed a standard or high-fat diet (HFD). Blood glucose and insulin levels were determined after glucose loads. Islet size, cleaved caspase-3, and PKC delta expression were estimated by immunohistochemistry. In isolated islet cells apoptosis was assessed with TUNEL/TO-PRO3 DNA staining and the mitochondrial potential by rhodamine-123 staining. Changes in phosphorylation and subcellular distribution of forkhead box class O1 (FOXO1) were analyzed by Western blotting and immunohistochemistry. RESULTS-PKC delta KN mice were protected from HFD-induced glucose intolerance. This was accompanied by increased insulin levels in vivo, by an increased islet size, and by a reduced staining of beta-cells for cleaved caspase-3 compared with wild-type litter-mates. In accordance, long-term treatment with palmitate increased apoptotic cell death of isolated islet cells from wild-type but not from PKC delta KN mice. PKC delta KN overexpression protected islet cells from palmitate-induced mitochondrial dysfunction and inhibited nuclear accumulation of FOXO1 in mouse islet and INS-1E cells. The inhibition of nuclear accumulation of FOXO1 by PKC delta KN was accompanied by an increased phosphorylation of FOXO1 at Ser256 and a significant reduction of FOXO1 protein. CONCLUSIONS-Overexpression of PKC delta KN in beta-cells protects from HFD-induced beta-cell failure in vivo by a mechanism that involves inhibition of fatty acid-mediated apoptosis, inhibition of mitochondrial dysfunction, and inhibition of FOXO1 activation. Diabetes 59:119-127, 2010